Converting ER Diagrams to a [[Relational Model]]

Last updated Dec 14, 2021 Edit Source

• Cs diagrams
• Cs databases

Even though ER Diagrams contain more semantic information, they are harder to turn into actual databases because some of the constraints are impossible to represent.

When you have an entitity without any relations connected to it, all you need to do is to create an entry in the schema with the given attributes.

With an N:M relationship, you need to create a new entry in the schema to represent that relation. Here is a more visual example:

In this case you just push the relationship information to the side with the * cardinality.

Same as the 1:M one, just need to pick a side to put the relation.

When attributes are attached to a relation, you simply add another attribute to the relation.

# Weak Entity and Identifying Relationship in ER Diagrams

Since weak entities are defined using the identifying relationship, you put the relationship in the weak entity.

You just flatten them

Treat the attribute as a relation and create a new relation with a cardinality of 1:N.

Create a single entity that contains all the attributes and relations from all types and add an extra attribute type.